1. Field of the Invention
The present invention relates to a method of manufacturing aromatic urethanes.
2. Description of the Related Art
U.S. Pat. No. 4,678,856 discloses a method wherein a primary aromatic amine, an aromatic nitro compound, and carbon monoxide are caused to react together in the presence of a specified catalyst and solvent to produce a N,N'-disubstituted urea, the urea obtained by this method in turn being caused to react with an organic compound containing hydroxyl groups to produce a primary aromatic amine and an aromatic urethane, the aromatic urethane then being separated and recovered from the reaction product. The above U.S. patent also discloses that aromatic amine is used as a solvent, the amount of which is over the quantity specified as being required for the reaction.
In U.S. patent application Ser. No. 07/825,822, an improvement of U.S. Pat. No. 4,678,856 is disclosed wherein nitriles, pyridines, quinolines and cyclic ethers are used as solvents to stabilize the catalyst and prevent it from separating out. Use of such solvents prevent the catalyst from separating out of the system together with crystals of the urea compound product, and permits the catalyst to be re-used.